Within some medical treatment areas a combination therapy involving co-administration of at least two active agents is advantageous because of synergistic or additive effects. For example, within diabetes care, in the management of type 2 diabetes mellitus, concomitant use of certain insulin and glp-1 products has been shown to reduce HbA1c levels in subjects, thereby improving glycaemic control.
Many drugs must be administered parenterally to be effective in the body and some of these, e.g. insulin and glp-1, may require one or more doses to be delivered subcutaneously on a daily basis. Subcutaneous drug delivery is often associated with discomfort as many people dislike the thought of having an injection needle inserted through the skin. An undisclosed number of people even suffer from needle-phobia, and these people have a particular strong desire to escape multiple daily injection therapy.
One attractive scenario, therefore, is to reduce the number of required skin penetrations by administering the injectable media at the same time, or substantially the same time. In that respect prefabricated mixtures of the involved media are not always an optimal solution. For one, some substances are only stable in mixed form short-term, and it may accordingly be necessary to keep those substances apart until just prior to administration. Adding to that, the individual subject users may have different needs in terms of dose ratios of the constituent active ingredients. Even a single subject user may sometimes require varying dose ratios of the active ingredients in a relatively short time span, e.g. during a titration period. It may thus not be feasible to cover all the individual needs by premixed pharmaceutical products.
U.S. Pat. No. 3,911,916 (Stevens) discloses an injection syringe for sequential injection of two or more medicaments through a single cannula. The syringe comprises a barrel which is partitioned by a number of plugs defining a number of medicament receiving compartments. By this arrangement it is possible to inject two or more medicaments at substantially the same time, thereby avoiding multiple cannula insertions. However, the syringe offers no flexibility with respect to the specific medicaments to be delivered in the sense that it is not possible to sequentially deliver other drugs than the ones already contained in the compartments. Furthermore, it is not possible to vary the volumetric ratios of the contained medicaments, which means that the syringe is only able to cover the needs of a certain group of subjects requiring a particular volumetric combination of the medicaments.
WO 2010/149736 (Sanofi-Aventis Deutschland GmbH) discloses a cannula arrangement for an injection device which cannula arrangement is adapted to contain a medication for co-delivery with a medication in the injection device. The cannula arrangement is adapted to be connected to the injection device and operated to expel the medicament contained therein just prior to a dose of medicament being expelled from the injection device. While this arrangement enables greater flexibility with respect to the specific medicaments to be delivered than the syringe disclosed in U.S. Pat. No. 3,911,916, the solution appears to have several drawbacks. The medicament in the cannula arrangement must be delivered by the application of a transversal force to a collapsible reservoir, whereafter an axial force must be applied to the injection device to deliver a dose of the medicament contained therein. This entails a rather complex delivery procedure which appears difficult to execute without the user having to change grip on the injection device along the way. Furthermore, it is virtually impossible to deliver the two medicaments in an exact volumetric ratio because even if the cannula arrangement could be emptied, which is difficult using a flexible reservoir, it is not possible to estimate, and account for, the degree of re-filling of the cannula reservoir during the subsequent flushing of the cannula arrangement with the medicament from the injection device. In other words, the dosing of at least one of the two medicaments will be subject to uncertainty.